1. Field of the Invention
The present invention relates to a high-frequency component using a coupling line, more particularly, to a high-frequency component using a coupling line, which is used as a coupler (directional coupler) in an IC for radio communication equipment, a phased converter, and a balun (balance/unbalance signal converter).
2. Description of the Related Art
A balun (balance/unbalance converter) is exemplified as a high-frequency component using a coupling line. The balun mutually converts a balance signal of a balance transmission line and an unbalance signal of an unbalance transmission line. Note that the balance transmission line means having two signal lines which become a pair and transmitting a signal (balance signal) as an electrical potential between the two signal lines and, on the contrary, the unbalance signal means transmitting a signal (unbalance signal) as an electrical potential of one signal line with respect to the ground potential (zero potential), for example, a coaxial line or a microstrip line provided on a substrate.
FIG. 15 shows one example of a conventional laminating type balun. A laminating type balun 120 comprises: a dielectric layer 122c provided with a lead electrode 121 on the surface thereof; a dielectric layer 122d provided with a xc2xd-wavelength strip line 123 having a spiral portion on the surface thereof; a dielectric layer 122e provided with xc2xc-wavelength strip lines 124 and 125 like spiral forms on the surface thereof; dielectric layers 122a and 122y provided with shielding electrodes 126 and 127 on the surface thereof, respectively; dummy dielectric layers 122b and 122f; and the like. The strip lines 124 and 125 are electro-magnetically coupled to a right portion 123a and a left portion 123b of the strip line 123. That is, the strip lines 124 and 125 constructing the balance transmission line are electro-magnetically coupled to the strip line 123 constructing the unbalance transmission line throughout the substantially entire length of the strip lines.
According to the conventional balun 120, the layer thickness of the dielectric layer 122d is changed, thereby adjusting the electro-magnetic coupling degree between the strip lines 124 and 125 and the strip line 123. Therefore, the layer thickness of the dielectric layer 122d must be made thick when manufacturing a product whose electro-magnetic coupling degree is loose between the strip lines 124 and 125 and the strip line 123 and, thus, the miniaturization is difficult.
If increasing a characteristic impedance of the balun 120, it is necessary to narrow the line widths of the strip lines 123 to 125 and narrow the line interval of the spiral portion. Thus, a printing technique at a high level is required to form the strip lines 123 to 125. Further, when narrowing the line widths of the strip lines 123 to 125, resistivities of the strip lines 123 to 125 rise and a problem to increase the insertion loss also arises.
Then, it is an object of the present invention to provide a high-frequency component using a coupling line with a small size, capable of easily adjusting an electrical characteristic.
In order to attain the object, according to the present invention, there is provided a high-frequency component using a coupling line which has a first transmission line and a second transmission line, at least one coupling portion for mutually coupling the first transmission line and the second transmission line electro-magnetically, and at least three line sections to which the first transmission line and second transmission line in the coupling portion are serially connected electrically, wherein line sections on one end sides of the first transmission line and the second transmission line in the coupling portion are mutually coupled electro magnetically, and the line sections on another-end sides of the first transmission line and the second transmission line are mutually coupled electro-magnetically. As the high-frequency component using the coupling line, a coupler or balun, etc. is exemplified.
According to the above-discussed construction, even in a central portion in the first transmission line in the coupling portion is not faced to a central portion in the second transmission line in the coupling portion, both end portions of the first and second transmission lines are coupled electro-magnetically. This causes a phase of a signal transmitted through the second transmission line to be shifted by a desired amount of phase difference with respect to a phase of a signal transmitted through the first transmission line.
Further, as compared with a case of electro-magnetically coupling the first transmission line and the second transmission line by the entire lines thereof, the electro-magnetic coupling degree between the first and second transmission lines is decreased. Therefore, when designing a loose electro-magnetic coupling, it is unnecessary to increase a distance between the first and second transmission lines in the coupling portion. In case of a high-frequency component with a laminating structure, it is able to reduce a thickness of the dielectric layer between the conductive patterns, which are mutually coupled electro-magnetically, and to reduce the height of the high frequency component.
By connecting a capacitor for impedance adjustment to an input terminal or output terminal of the first transmission line or second transmission line, it is possible to match desired input/output impedances corresponding to an impedance of an external circuit.